Walker may not think that there is much to document, but “Out of Focus” — which screens at the Kendall Square Cinema before his sold-out show at the Sinclair on Wednesday — provides an interesting snapshot of the musician’s life. Peter Harding and Shane Valdes head to London and Los Angeles as Walker toured and recorded his most recent and splendid full-length album, “The Spade,” with his sometime band the Black Widows. The film also offers a peek into his family life.

Beyond that snapshot there is plenty to talk about when it comes to the Atlanta-bred musician, who over the course of a varied, 20-plus-year career is one of those “best kept secrets” in the music business. (Walker divulged some of his own secrets in his funny, candid 2011 book, “Drinking With Strangers.”)

After a stint prowling the Sunset Strip in the hard rock band SouthGang in the early ’90s, he transitioned to the power pop trio Marvelous 3 and hit the charts with “Freak of the Week.” Walker then began carving out concurrent careers as a solo artist with a devoted cult following swayed by his insightful, tuneful pop-rock storytelling and as an in-demand songwriter-producer with a mass of hits to his credit with artists across the pop-rock-country spectrum from Pink and Katy Perry to Fall Out Boy and Weezer to Taylor Swift and Keith Urban.

None of those famous folk pop up in “Out of Focus,” however, since Walker prefers to keep a church-state separation between his two lives, and instructed the filmmakers to do the same.

“I’m already the bad guy here because this is going to look like a full-on exercise in narcissism and I didn’t want some documentary about, ‘Who the [expletive] is this guy anyway?’ ,” he says. “The fact that I am still an artist first and foremost, but just not as famous and popular as the people that I write with and produce, I’m really touchy about [mixing the two]. I don’t want people to think I’m trying to co-opt on other people’s celebrity for my own career. That just feels gross to me. The last thing I wanted to do was get these endorsements. I’m not trying to prove anything to anybody,” he says.

Walker may not have been interested in testimonials, but there are plenty of people eager to sing his praises.

“He’s very eclectic, wonderfully so,” says Urban, who coproduced four tracks and co-wrote one with Walker on his just-released album, “Fuse.” “He has great melodic instincts and his backing vocal parts are just celestial, they’re beautiful.”

“I would 100 percent say this comeback would not have happened without Butch,” says Pete Wentz of his band Fall Out Boy’s recent reunion album, “Save Rock and Roll,” which Walker produced. “We realized that we needed someone who could adapt the intangible things that people fell in love with about Fall Out Boy, but do it in a completely different sonic way for 2013. And for us it was really important for that to be Butch Walker, because it needed to be somebody that we respected.”

(Incidentally, it was a song on that record that caused Urban to track down Walker.)

Like most Walker devotees, Wentz is also mesmerized by Walker’s live shows, which he plays with an almost maniacal energy. And like many Walker fans, Wentz appreciates the distinctions Walker makes between his own music and the music of those with whom he collaborates.

“I’ve known him for probably 10 years and there’s something so pure and magical about the Butch Walker experience that I wouldn’t want him to twist it around so it could fit into a more mainstream vision,” says Wentz.

Famous friends or not, Walker is ultimately glad that “Out of Focus” came to be.

“I was ready to cringe because watching yourself for an hour and a half is cringe-worthy. But I thought it turned out pretty good,” he says, pleased it’s not a vanity piece. “There’s plenty of people talking smack and I’m happy about that. It wasn’t about praising, it was more about the everyday struggle of trying to keep a band together, a family together, your dad alive.

“I was really touched by the footage of my family and some things that were said and I thought, if anything, this will be a nice little thing to just have as a keepsake for my family and my son one day when he’ll appreciate it.”

Especially given that Walker’s dad, “Big” Butch — his son’s biggest fan and best friend — passed away just a few weeks ago. The senior Walker’s failing health is something on which Walker ruminates on his forthcoming EP “Peachtree Battle,” which will be available digitally Sept. 17 and on vinyl Oct. 22.

“My dad’s always been the king of good timing so, in a way, I think it was poetic that he passed right before [the film] came out and also before the new record came out because a lot of the songs on there were either literal or metaphoric for coming to terms with his mortality,” says Walker.

Although still grieving, Walker is taking to the road to work it out with his other family, the fans whom he affectionately likens to “the island of misfit toys.” The stage is a place he needs to be.

“It feeds a part of my soul that will never be fed by punching buttons on a console.”

BostonGlobe.com complimentary digital access has been provided to you, without a subscription, for free starting today and ending in 14 days. After the free trial period, your free BostonGlobe.com digital access will stop immediately unless you sign up for BostonGlobe.com digital subscription. Current print and digital subscribers are not eligible for the free trial.

Thanks & Welcome to Globe.com

You now have unlimited access for the next two weeks.

BostonGlobe.com complimentary digital access has been provided to you, without a subscription, for free starting today and ending in 14 days. After the free trial period, your free BostonGlobe.com digital access will stop immediately unless you sign up for BostonGlobe.com digital subscription. Current print and digital subscribers are not eligible for the free trial.